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  Brushless motorUSPTO Application #: 20060006747Title: Brushless motor Abstract: A drive/control circuit integrated brushless motor is provided that has high rotating precision, satisfactory noise resistance and high output, and is suited to be smaller to save as much space as possible. The motor is a brushless motor provided with circuit integrated core with an FG pattern formed uniformly along the entire circumference by including a pattern system FG, and arranging a Hall element on a surface of a circuit substrate opposite the surface formed with the FG pattern and a noise cancel pattern. (end of abstract) Agent: Steptoe & Johnson LLP - Washington, DC, US Inventor: Koji Kadowaki USPTO Applicaton #: 20060006747 - Class: 31006800B (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20060006747. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention relates to a brushless motor used as a main motor for simultaneously driving various mechanisms such as a copying machine and a laser beam printer. More particularly, the invention relates to a brushless motor including a stator core (iron core) around which a stator coil is wound, a rotor attached with a ring-shaped magnet, a Hall element for detecting the position of the rotor, and a speed detector for detecting the rotating speed of the rotor, and integrally incorporating a drive/control circuit for rotatably driving and controlling the rotor and a motor. [0003] 2. Description of the Related Art [0004] Recently, document products such as a copying machine and a laser beam printer are oriented to have high image quality, high-speed printing and coloring, and to simultaneously realize such, tend to use a so-called tandem system that includes a photosensitive drum for each color. The conventional configuration including one drum now is a configuration including two drums or four drums, and thus the apparatus unavoidably becomes larger. To suppress such enlargement, however, the main motor for driving various mechanisms is required to be thinner, smaller, to save as much space as possible, and to have high output. [0005] The brushless motor integrally incorporating a motor section including a stator equipped with a stator core (iron core) suitable for high output, and a drive/control circuit for rotatably driving and controlling the motor is generally used as the main motor, and the entire motor including the circuit section is required to be thinner, smaller, to save as much space as possible, and to have high output. [0006] To this end, the outside dimension of the stator part of the motor section and the circuit section is desirably made as close as possible to the dimension of a square circumscribing the rotor part, and similarly, the height dimension is desirably made as close as possible to the height dimension of the rotor part. [0007] Conventionally, the well-known brushless motor including the stator core (iron core) includes a rotor in which a ring-shaped magnet having a plurality of magnetic poles facing the stator core (iron core) is provided on the inner peripheral surface of the rotor yoke and a stator assembly in which the stator coil (armature coil) is wound around each stator core (iron core). The stator assembly is attached to a circuit substrate (stator base) equipped with a Hall element (position detecting element) and a drive circuit for rotatably driving the rotor by way of a housing (bearing holder). The rotating position of the rotor is detected by detecting the magnetic pole of the magnet of the rotor with the Hall element (position detecting element), and from the drive circuit to where the output signal of the Hall element is input, the drive current controlled in accordance with the output signal of the Hall element (position detecting element) is supplied to the stator coil (armature coil). The stator coil (armature coil) then generates a magnetic field corresponding to the rotating position of the rotor. The rotor is configured (hereinafter referred to as a first conventional art) so that a continuous rotating force is generated by the interaction of the magnetic field generated by the stator coil (armature coil) and the magnetic pole of the magnet (refer to e.g., JP-A 8-88964 (1996).). [0008] FIG. 6 shows a configuration of a conventional brushless motor. [0009] In FIG. 6, reference character 1 refers to a shaft, reference character 2 refers to a rotor yoke, reference character 3 refers to a magnet, reference character 4 refers to a stator coil (armature coil), reference character 5 refers to a stator core (iron core), reference character 6 refers to a Hall element (position detecting element), reference character 7 refers to a drive circuit, reference character 8 refers to a circuit substrate (stator base), reference character 9 refers to a bearing, and reference character 10 refers to a housing (bearing holder). [0010] In the conventional brushless motor, the Hall element 6 is arranged at a position where the magnetic flux of the magnet 3 of the rotor is easily picked up, that is, on the inner diameter side of the magnet 3 on the surface side facing the magnet 3 of the circuit substrate (stator base) 8 to obtain the output necessary for position detection from the Hall element (position detecting element) 6. When arranged at such position, however, the Hall element (position detecting element) 6 is also arranged close to the stator coil (armature coil) 4, and thus the magnetic field generated by the excitation of the stator coil (armature coil) 4 influences the Hall element 6 as a noise, and a stable position detection may not be performed. [0011] As high output is required, particularly, in the brushless motor used as a so-called main motor for simultaneously driving various mechanisms such as a copying machine and a laser beam printer, a large amount of current must flow to the stator coil (armature coil) 4. If the drive current is increased, however, the magnetic field generated at the stator coil (armature coil) 4 becomes large, which generated magnetic field influences the Hall element 6, thereby making a stable position detection difficult. [0012] As shown in FIG. 7, a solution for the above problem includes a technique (hereinafter referred to as a second conventional art) for preventing the magnetic field generated by the excitation of the stator coil (winding wire) 4 from influencing the Hall element (detecting element) as noise with a configuration in which one portion of the magnet 3 arranged in the rotor yoke 2 is exposed from the rotor yoke 2, the Hall element (detecting element) 6 is arranged exterior to the magnet 3 in correspondence to the exposed portion of the magnet 3, and the leakage flux of the exposed portion of the magnet is detected (refer to e.g., JP-A 8-172763 (1996)). [0013] Further, a solution different from the second conventional art includes a technique (hereinafter referred to as a third conventional art) in which the magnetic field generated by the excitation of the stator coil (driving coil) 4 is assumed to influence the output waveform of the Hall element (position detecting element) 6 thus producing deformation at a zero cross point of the output waveform, the deformation being produced in a direction that delays the current feed switching timing toward the stator coil (driving coil) 4, and as shown in FIGS. 8 and 9, a driving magnet 3a and a position detecting magnet 3b are arranged as the magnet (driving magnet) 3 of the rotor in such a way that the boundaries where the magnetic poles are opposite poles with respect to each other contact, thereby eliminating the delay of current feed switching by inversing the output of the Hall element (position detecting element) 6 so that the deformation of the output waveform is produced in a direction that accelerates the current feed switching toward the stator coil (armature coil) 4 (refer to e.g., JP-A 7-327351 (1995)). [0014] More specifically, as shown in FIG. 9, the driving magnet 3a and the position detecting magnet 3b are arranged on the magnet (driving magnet) 3 of the rotor in such a way that the boundaries where the magnetic poles are opposite poles with respect to each other contact. Further, the Hall element (position detecting element) 6 is arranged on the circuit substrate (substrate) 8 at a position facing both the position detecting magnet 3b and the stator core 5 with which the stator coil (driving coil) 4 is wound. The planar arrangement of the Hall element 6 is configured as shown in FIG. 10, where the Hall element (detecting element) 6U of U phase, the Hall element (detecting element) 6V of V phase, and the Hall element (detecting element) 6W of W phase are arranged in correspondence to the each teeth of the U phase, the V phase and the W phase of the stator core (iron core) 5. The arrow indicates the direction of rotation. [0015] According to this configuration, the composite magnetic field of the magnetic field generated by the excitation of the stator coil (driving coil) 4 and the magnetic field of the position detecting magnet 3b is detected by the Hall element (position detecting element) 6, thereby eliminating the delay of current feed switching toward the stator coil (driving coil) 4. [0016] FIGS. 11A to 11G (FIGS. 9A to 9G of JP-A 7-327351 (1995)) shows that the magnetic field of the U phase and the W phase generated by the excitation of the stator coil (winding wire) 4 influences the output waveform of the Hall element (detecting element) 6U of the U phase, thus producing deformation at the zero cross point of the output waveform. The deformation is produced in a direction that delays the current feed switching timing toward the stator coil (driving coil) 4. FIG. 11A is the generated magnetic field of the driving magnet toward the Hall element (detecting element) 6U, FIG. 11B is the generated magnetic fields of the U and W phase cores, FIG. 11C is the generated magnetic field of the U and W phase cores toward the Hall element (detecting element) 6U, FIG. 11D is the generated magnetic field of the composite cores of U and W phases toward the Hall element (detecting element) 6U, FIG. 11E is the output waveform of the Hall element (detecting element) 6U, FIG. 11F is an enlarged view of the horizontal axis of the main part of FIG. 11E, and FIG. 11G is the generated magnetic field of the actual W phase core. [0017] FIGS. 12A to 12E (FIGS. 3A to 3E of JP-A 7-327351 (1995)) show that the output of the Hall element (position detecting element) is inversed and the deformation of the output waveform is produced in a direction that accelerates the current feed switching toward the stator coil (driving coil). FIGS. 12A and 12B show the magnetic field toward the Hall element (detecting element) 6U and the magnetic field toward the core, FIG. 12C shows an output waveform of the Hall element (detecting element) 6U, FIG. 12D shows an enlarged view of the horizontal axis of the main part of FIG. 12C, and FIG. 12E shows an enlarged view of the generated magnetic field of the W phase core. [0018] In the brushless motor used as the main motor for simultaneously driving various mechanisms such as a copying machine and a laser beam printer, not only the rotating speed of the motor, but the rotating phase in relation with the various mechanism sections of the apparatus driven by way of an output shaft and a decelerating mechanism attached to the output shaft must also be accurately controlled. Thus, the brushless motor requires a speed detector having a certain degree of resolution. [0019] The speed detector of the brushless motor suited for the above application includes a so-called pattern FG system. The ring-shaped FG magnet subjected to NS multi-pole magnetization along the circumferential direction is arranged on the rotor side, the FG pattern including the generator wire elements of the same number as the magnetized poles of the FG magnet connected in series along the circumferential direction is arranged on the stator side, and the speed detecting signal (FG signal) of the frequency proportional to the rotating number of the motor produced in the FG pattern by the rotation of the motor is obtained. When incorporating the speed detector of the FG pattern system in the brushless motor, a configuration in which the driving magnet of the motor and the FG magnet are integrated by performing magnetization for the driving magnet on the inner peripheral side of the rotor magnet and NS multi-pole magnetization for the FG magnet (hereinafter referred to as FG magnetization) on the end face side, and the FG pattern is formed on the circuit substrate of the motor is desirable as a configuration with no influence on the shape of the motor and no additional component. [0020] However, in either of the second conventional art and the third conventional art, an adverse effect arises due to performing FG magnetization on the end face on the circuit substrate (substrate) side of the magnet (driving magnet) of the rotor. [0021] That is, the Hall element (position detecting element) must be arranged in the vicinity of the end face on the circuit substrate (substrate) side of the magnet (driving magnet) of the rotor, and thus the influence of FG magnetization formed on the end face of the magnet (driving magnet) of the rotor cannot be avoided, and a stable position detection becomes difficult. [0022] In the second conventional art, the influence of FG magnetization can be prevented by spacing the Hall element (position detecting element) away from the magnet (driving magnet) of the rotor to an extent the influence of FG magnetization can be neglected with the dimension of one portion of the magnet of the rotor exposed from the rotor yoke being sufficiently large to an extent the influence of the FG magnetization can be neglected, but when the exposed portion of the driving magnet is large, the leakage flux increases thus increasing loss or unnecessary magnetic noise. Alternatively, the influence of FG magnetization can be prevented by attaching the Hall element (position detecting element) so as to float from the surface of the circuit substrate (substrate) by a certain extent, but this may increase the attachment cost and the like of the Hall element (position detecting element). [0023] The third conventional art acts counter to the technically necessary configuration, and thus the FG magnetization becomes impossible to be performed on the end face of the circuit substrate (substrate) side of the magnet (driving magnet) of the rotor. Continue reading... Full patent description for Brushless motor Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Brushless motor patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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